Threatening letters containing poisonous ricin sent to Mayor Bloomberg and his anti-gun group said "what's in this letter is nothing compared to what I've got planned for you," police and law enforcement sources said.
One letter was discovered at the city's mail sorting location at 100 Gold St. at about 2 p.m. Friday, a law enforcement source told NBC 4 New York. It appeared to contain a pink, oily substance when a mail worker came across it and was immediately flagged as suspicious.
An initial field test didn't bring up any sign of ricin, a source said. But more preliminary testing Wednesday showed the letter tested positive for ricin.
An identical letter containing ricin was sent to the Mayors Against Illegal Guns headquarters in Washington, D.C. and was opened on Monday, police said.
According to law enforcement sources, both letters were postmarked May 20 in Shreveport, La. and sent without a return address or signature. Sources said the NYPD tried to pull fingerprints off the letter discovered at the city's mail sorting site, but nothing usable was found. Authorities also plan to check for any possible DNA.
It wasn't known if any viable forensic evidence was discovered on the letter sent to Washington. Both mailings read in part: "You will have to kill me and my family before you get my guns. Anyone wants to come to my house will get shot in the face. The right to bear arms is my constitutional God given right and I will exercise that right till the day I die."
Bloomberg is the founder of the anti-gun group and has emerged as one of the country's most potent gun-control advocates, able to press his case with both his public position and his private money.
On Wednesday, the mayor said he didn't know what pushed whoever sent the ricin-laced letters to do so, but that his anti-gun efforts would not be deterred, despite the threats in the letter addressed to him.
"There's 12,000 people that are going to get killed this year with guns and 19,000 that are going to commit suicide with guns, and we're not going to walk away from those efforts," said Bloomberg, adding that he didn't "feel threatened."
Civilian workers who came into contact with the letters have not shown symptoms of being poisoned by the ricin, police said. Some members of NYPD's emergency service unit who did come into contact with the opened letter in New York initially showed some minor symptoms of ricin exposure, but the symptoms have since abated.
According to the Centers for Disease Control, ricin is a poison found naturally in castor beans. Symptoms can include difficulty breathing, vomiting and redness on the skin depending on how the affected person comes into contact with the poison.
The FBI and NYPD are investigating the threats. Law enforcement officials are also looking to see if other similar letters were sent to the White House, members of Congress or other government offices as a precaution.
The letters were the latest in a string of toxin-laced missives. In Washington state, a 37-year-old was charged last week with threatening to kill a federal judge in a letter that contained ricin. About a month earlier, letters containing the substance were addressed to President Barack Obama, a U.S. senator and a Mississippi judge. A Mississippi man was arrested in that case.
Police said the letter in Washington, D.C., was opened by Mark Glaze, the director of Mayors Against Illegal Guns. He was working out of the offices of The Raben Group, a Washington lobbying firm where he keeps an office. Glaze happened to open the letter while sitting outside over the Memorial Day weekend, said the firm's founder, Robert Raben.
"I'm very concerned about our employees and co-workers and clients. I'm sorry that we live in a world in which people do such awful things. Thank God, right now, everybody's physically fine," Raben said by phone Wednesday, adding that the firm would do whatever needed to ensure safety.
A mayor's spokesman also speaking for the nonprofit said he had no comment.